I have a portable battery pack that will start my diesel with a completely dead battery, much easier than playing around with jumper cables (about $150 at the local McParts place).

How do you make a "good" connection with that pack?

Just a couple of heavy jumper cable type clamps, good enough I guess. I bought it and used it when my alternator died in TX last year and my battery was so dead that the dash lights and the gauges would not work. You definitely need to get a good connection.

This might be a successful endeavor at 50F or more. I don't think it would be successful at 20F. The required amperage to rotate the engine is much greater and the capability of the cold pack is much less.

Maybe, I haven't tried. I mostly carry the thing to help other people. If/when my alternator/battery dies again I'll give it a try. I still have some very heavy jumper cables in the trunk that I have used in 0F temperatures, but the battery pack is much easier.

I'd like to know how you make out at very low temps. My thought has always been that the four points on the clamp are the limiting factor...........but, the cable may also be significant.

Hopefully I'll never find out (new-ish battery and alternator at the moment), but if I have a chance to try it in the cold I'll let you know what happens.